A thermal insulator bottle formed mainly of an evacuated double glass tube, which is often called a thermos bottle, is designed to keep the temperature of a liquid contained therein constant for a longer period both be preventing heat transmission due to conduction and convection and by reflecting radiant heat. However, the time during which the temperature of the liquid is kept constant is limited so that even boiling water gets cold with the lapse of time. In this connection, the lower the ambient temperature, the larger the cooling rate will be. This results from the fact that the conventional thermos bottle is constructed taking aim at insulating heat without any additional heating/cooling means.